The sizes of the discrete components that make up semiconductor devices have consistently been scaled down for more than 20 years. The benefits obtained by shrinking component size include enhanced device performance and high clock frequencies.
As semiconductor devices are scaled down in size, the width and spacing of interconnects connecting the components of the devices are also scaled down. Smaller and smaller interconnect dimensions lead to a number of problems. For example, closer spacing between conductive lines results in a rise in parasitic capacitance between multiple semiconductor layers and within a single layer. An increasing parasitic capacitance increases the RC (resistance-capacitive) delay associated with the device, which limits the length of global routing lines and tends to slow down the device. Further, as the pitches of lines in the device are reduced, undesirable cross-talk between the lines increases.
A semiconductor layer known as an interlayer dielectric (ILD) layer is a layer formed between multiple active layers of a semiconductor device. One known approach to reducing RC delay and cross-talk effects between multiple semiconductor layers involves decreasing the dielectric constant (k) of the ILD layer. Conventional attempts at reducing the dielectric constant of the ILD typically form the ILD layer from a polymer, such as, hydrogen silsesquioxane (HSQ), parylene, polyimide, or amorphous Teflon.
In an article by K. Yoshiyama et al., "A Simple Sub-0.3 .mu.m CMOS Technology with Five-Level Interconnect using Al-plug and HSQ of Low-k for High Performance Processor", 1997 Symposium on VLSI Technology Digest of Technical Papers, pp. 55-56, there is disclosed a sub-0.3 micron CMOS technology that has a five-level interconnect structure which uses aluminum plugs and a low dielectric constant HSQ film. The interlayer dielectric film of the Yoshiyama device comprises a thin plasma TEOS (tetraethylorthosilicate) film and an HSQ film formed on the TEOS film by a spin-on method. The gap-filling properties of the HSQ film and the consequent reduction of parasitic coupling capacitance in the Yoshiyama device was reported as excellent. More particularly, the parasitic coupling capacitance was reduced by more than 10% compared to conventional devices.
Additional descriptions of the formation of low dielectric (low-k) ILD layers can be found in U.S. Pat. No. 4,756,977 to Haluska et al. and U.S. Pat. No. 5,320,868 to Ballance et al. More particularly, Haluska et al. describe a method for forming a low-k dielectric film by diluting in a solvent a HSQ resin solvent solution, which is applied to a substrate and transformed into a ceramic by heating.
The above-discussed conventional methods for forming a low-k dielectric film generally produce a predominantly Si--O--H dielectric film structure. The hydrogen (--H) in the Si--O--H structure of such a low-k dielectric film has been found to be very reactive with gases such as CHF.sub.3 and CF.sub.5 used in subsequent dry etching steps for forming a contact via in the dielectric layer. Consequently, the etching profile of an HSQ film with a low-k dielectric tends to exhibit a bowing effect.
FIG. 1 is a cross-section of an ILD layer formed with conventional techniques. Layers 105 and 107 are dielectric layers having a dielectric constant different from that of the ILD layer 106. The bowing effect 110 in the etching profile of the low-k oxide ILD layer 106 can result in a void 112 being created when a metal plug 111 is formed so as to electrically interconnect the upper conductive layer 108 and the lower conductive layer 109. The void 112 deteriorates the electrical conductivity of the interconnections. Furthermore, the reaction of hydrogen in the ILD layer with gases during the dry etching process can generate defects on the surface of the dielectric film.